The United Nations Intergovernmental Panel on Climate Change (IPCC) has been leading the effort in collecting scientific evidence of climate change and in looking to answer the most important question, is it caused by human activity? Some argue that it is caused mostly by natural variability, and non-human factors. The new IPCC report, released this week, provides more evidence that human activity is a major cause.

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The UN is calling for a global response to combat climate change, following new findings by the IPCC stating it is "extremely likely" that humans have been the dominant cause of unprecedented global warming since 1950."The heat is on. Now we must act," Secretary-General Ban Ki-moon said in a video message to the launch of the report of the UN-backed IPCC.

"This new report will be essential for Governments as they work to finalize an ambitious, legal agreement on climate change in 2015," Mr. Ban said. "The goal is to generate the political commitment to keep global temperature rise below the agreed 2-degree Celsius threshold."The IPCC report, released today in Stockholm, Sweden, calls global warming "unequivocal," and confirms that there is a 95 per cent probability that most of the warming since 1950 has been caused by human influence.

The report stresses that evidence for this has grown "thanks to more and better observations, an improved understanding of the climate system response and improved climate models."

"The IPCC report demonstrates that we must greatly reduce global emissions in order to avoid the worst effects of climate change," said the Secretary-General of the World Meteorological Organization (WMO), Michel Jarraud. "It also contains important new scientific knowledge that can be used to produce actionable climate information and services for assisting society to adapt to the impacts of climate change."

In its report, the IPCC notes that continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. It adds that limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.

"Climate change is a long-term challenge but one that requires urgent action, not tomorrow but today and right now, given the pace and the scale by which greenhouse gases are accumulating in the atmosphere and the rising risks of a more than 2-degree Celsius temperature rise," said the Executive Director of the UN Environment Programme (UNEP), Achim Steiner.